This disclosure relates to maintaining print quality in xerographic developer systems. More particularly, the teachings herein are directed to apparatus and methods for driving one or more donor rolls in a developer system.
Generally, the process of electrophotographic printing includes charging a photoconductive member such as a photoconductive belt or drum to a substantially uniform potential to sensitize the photoconductive surface thereof. The charged portion of the photoconductive surface is exposed to a light image from a scanning laser beam, a light emitting diode (LED) source, or other light source. This records an electrostatic latent image on the photoconductive surface. After the electrostatic latent image is recorded on the photoconductive surface, the latent image is developed in a developer system with charged toner. The toner powder image is subsequently transferred to a copy sheet and heated to permanently fuse it to the copy sheet.
The electrophotographic marking process given above can be modified to produce color images. One electrographic marking process, called image-on-image (IOI) processing, superimposes toner powder images of different color toners onto a photoreceptor prior to the transfer on the composite toner powder image onto a substrate, such as paper. While the IOI process provides certain benefits, such as a compact architecture, there are several challenges to its successful implementation. For instance, the viability of printing system concepts, such as IOI processing, require developer systems that do not interact with previously toned images.
In the developer system, two-component and single-component developer materials are commonly used. A typical two-component developer material comprises magnetic carrier granules having toner particles adhering triboelectrically thereto. A single-component developer material typically comprises toner particles. Since several known developer systems such as conventional two component magnetic brush development and single component jumping development interact with the photoconductive surface, a previously toned image will be scavenged by subsequent developer stations if interacting developer systems are used. Thus, for the IOI process, there is a need for a scavengeless or noninteractive developer systems such as the Hybrid Scavengeless Development (HSD).
In scavengeless developer systems such as HSD, developer materials are maintained in a reservoir and conveyed onto the surface of a conventional magnetic brush roll, also referred to as a mag roll, based on a magnetic field necessary to load the mag roll. Toner is conveyed from the surface of the mag roll onto a donor roll. The donor roll is held at an electrical potential difference relative to the mag roll to produce the field necessary to load toner from the surface of the mag roll onto the surface of the donor roll. The toner layer on the donor roll is then disturbed by electric fields from a wire or set of wires to produce and sustain an agitated cloud of toner particles, which are attracted to the latent image to form a toner powder image on the photoconductive surface.
In donor roll based development systems, the donor roll or rolls are typically driven by one or more motors through a gear train. Since any donor roll velocity error, sometimes referred to as speed jitter, can modulate image development and result in print banding, typical developer systems utilize quality servo motors and precise gearsets to drive the donor roll or rolls. While such drive components have been successful in reducing print banding, speed jitter can occur under some conditions resulting in print banding.
While specific embodiments are described, it will be understood that they are not intended to be limiting. For example, even though the example given is a color process employing Image-On-Image technology, the disclosure is applicable to any system having donor rolls, as well as any other roll or element where it is desirable to reduce speed jitter.
These and other objects, advantages and salient features are described in or apparent from the following detailed description of exemplary embodiments.